We put the mac longtubes on a couple V6 cars, and they work real well. If you use the copper gaskets they send with the headers, I would make darn sure they are very tight. I usually use that red high temp, O2 safe silicone and then tighten them down, without gaskets, and they never leak.
Also, did you know the back of that engine is the same bolt pattern on the bellhousing as a 5.0? It's pretty cool because you can run a V8 trans behind it and loose the crappy sc trans.
Post up some pics man, i want to see this come together.